TH71221 datasheet(19/44 Pages) MELEXIS

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TH71221

27 to 930MHz

FSK/FM/ASK Transceiver

39010 071221

Page 19 of 44

Data Sheet

Rev. 009

Nov/15

4.1.3 Modulation Type

Modulation type

ASK

FSK

ASK / FSK

4.1.4 LNA Gain Mode

LNA gain

high

low

GAIN_LNA

4.2

Programmable User Mode Operation

The transceiver can also be used in programmable user mode. After power-up the first logic change at pin

FS0/SDEN enters into this mode. Now full programmability can be achieved via the Serial Control Interface

(SCI).

4.2.1 Serial Control Interface Description

A 3-wire (SCLK, SDTA, SDEN) Serial Control Interface (SCI) is used to program the transceiver in program-

mable user mode. At each rising edge of the SCLK signal, the logic value on the SDTA pin is written into a

24-bit shift register. The data stored in the shift register are loaded into one of the 4 appropriate latches on

the rising edge of SDEN. The control words are 24 bits lengths: 2 address bits and 22 data bits. The first two

bits (bit 23 and 22) are latch address bits. As additional leading bits are ignored, only the least significant 24

bits are serial-clocked into the shift register. The first incoming bit is the most significant bit (MSB). To

program the transceiver in multi-channel application, four 24-bit words may be sent: A-word, B-word, C-word

and D-word. If individual bits within a word have to be changed, then it is sufficient to program only the

appropriate 24-bit word. The serial data input timing and the structure of the control words are illustrated in

Fig. 12 and 13.

Fig. 12: SCI Block Diagram

A - LATCH

ADDR DECODER

B - LATCH

C - LATCH

D - LATCH

A-word

‘’

B-word

D-word

C-word

24-BIT

SHIFT REGISTER

SDEN

SDTA

SCLK

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